1. Technical Field of the Invention
The present invention relates generally to an improved structure of a dustproof push-on switch used in electronic devices.
2. Background of Related Art
FIG. 8 shows a conventional push-on switch which generally includes the box-like resinous base 1, the terminals 2 and 4, the outer stationary contacts 3A and 3B, the central stationary contact 5, the movable contact 6, and the push button 7.
The movable contact 6 consists of the annular plate 6A and the central disc 6B. The annular plate 6A is in contact with the outer stationary contacts 3A and 3B. The central disc 6B is, as shown in FIG. 9(a), connected to the annular plate 6A through the bridge 6C and bent upward at the bridge 6C, as shown in FIG. 9(b), so that it may lie at a given interval away from an inner wall of the push button 7.
The push button 7 is made from rubber and includes the thin-walled dome 7A, the thick-walled flange 7B, the cylindrical protrusion 7C, and the small-diameter inner protrusion 7D. The push button 7 is fitted at the flange 7B in the curled peripheral wall 1A of the base 1 tightly, thereby avoiding the ingress of dirt and dust into the inside of the push button 7.
In operation, depression of the protrusion 7C of the push button 7 through the operating button 8 installed in, for example, an electronic device will cause, as shown in FIG. 10, the thin-walled dome 7A to be deformed elastically to bring the central disc 6B of the movable contact 6 into engagement with the central stationary contact 5 through the inner protrusion 7D, thereby establishing an electric connection between the outer stationary contacts 3A and 3B and the central stationary contact 5, that is, between the terminals 2 and 4.
The above conventional push-on switch, however, has the following drawbacks.
The electric engagement of the outer stationary contacts 3A and 3B with the annular plate 6A of the movable contact is, as apparent from the above, accomplished by the elastic pressure exerted on the annular plate 6A from the curled peripheral wall 1A of the base 1 through the flange 7B. Thus, too weak elastic pressure provided by the curled peripheral wall 1A will result in disconnection between the outer stationary contacts 3A and 3B and the annular plate 6A. Conversely, too strong elastic pressure will cause the annular plate 6A to be deformed, thereby resulting in a change in interval between the central disc 6B and the central stationary contact 5.
The elastic movement of the curled peripheral wall 1A occurring when the push button 7 is fitted into the base 1 may also cause the position of the movable contact 6 to be changed, thereby resulting in a change in interval between the inner protrusion 7D of the push button 7 and the central disc 6B.
Further, if a circuit board collides with an upper portion of the protrusion 7C horizontally, as shown in FIG. 11, during installation of the push-on switch in an electronic device, for example, it may cause the flange 7B of the push button 7 to be moved out of engagement with the curled peripheral wall 1A, resulting in removal of the push button 7 from the base 1.